Radon decay has previously been studied and the typical decay pathway is known. Radon itself a decay product from uranium and thorium. There are some hundreds of publications devoted to earthquake research and a significant fraction of these include the measurement of radon (222Rn) (Friedman, 2010, Klusman et al., 1981, Mogro-Campero, 1980). Studies include seismic velocity changes, tilting of the earth's surface, strain accumulation, soil gas helium, mercury, radon emanation rate and radon increase in ground water. Changes in soil gas radon and groundwater are measured indicators. As yet there are no measurements of thoron (220Rn) emanation rate as a predictor of stress accumulation in soil.